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SubjectRe: Pinmux bindings proposal V2
On Fri, Jan 27, 2012 at 07:43:36AM -0800, Simon Glass wrote:
...
> The cost of the pmx@dta node is about 12 bytes for the header (it
> depends on the length of the name), and each of the properties above
> is 16 bytes. So in total this node is 76 bytes. If we have 250 pins
> being muxed as Tegra3 then this is about 20KB (including a bit of
> slack for longer names). My point about being able to 'optimise out'
> some of these remains, though, but probably not for the kernel.
>
> Stephen's 'mux' property uses 12 bytes plus 8 bytes per pin/group (I
> am removing the prefixes):
>
> mux =
> <PG_DTA MUX_SDIO1>
> <PG_DTD MUX_SDIO1>;
>
> so 28 bytes. What I proposed would use (12 + 2 * 16) per pin/group, or
> 44 bytes (60% bigger):
>
It's not only about size but also run-time tree travelling efficiency.
Your proposal requires every single pin show as a node in device tree.
Looking at these for_each_node_by_*() APIs in include/linux/of.h, you
might agree we should avoid bloating device tree with so many nodes.

--
Regards,
Shawn


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